1. Limited Copyright Waiver
A portion of the disclosure of this patent document contains computer code listings and command formats to which the claim of copyright protection is made. The copyright owner has no objection to the facsimile reproduction by any person of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but reserves all other rights whatsoever.
2. Field of the Invention
The present invention relates generally to data storage systems, and more particularly to a snapshot copy facility for a data storage system.
3. Description of the Related Art
Snapshot copies of a file system have been used for a variety of data processing and storage management functions such as storage backup, transaction processing, and software debugging. A snapshot copy facility, for example, stores a plurality of snapshot copies of a production file system. Each of the snapshot copies is a prior state of the production file system at a respective point in time. The snapshot copy facility has a bit map, a block map, and a save volume for each snapshot copy. The bit map for each snapshot copy indicates blocks of data in the production file system that have changed between the snapshot copy and a next snapshot copy of the production file system. The save volume for each snapshot copy stores the “before images” of the blocks that have changed between the snapshot copy and the next snapshot copy of the production file system. The block map for each snapshot copy provides the save volume block address given the block address of a block that has changed between the snapshot copy and the next snapshot of the production file system.